The present invention concerns a method for providing a sealed electrical connection of non corrodible anodes to the corrodible conductive core of a power supply cable.
The anodes used for the cathodic protection of buried or immersed metal structures, by the impressed current system, often need to be placed at a great distance from the surface of the structure to be protected, in order to ensure the best uniformity of current distribution over the structure itself.
Therefore, the electric current must be led to the anodes by electric cables exhibiting a low ohmic drop, such as insulated copper or aluminum cables. Said highly conductive metals, however, readily undergo anodic dissolution, if they come in contact with the medium, either water or soil, wherein the anodes operate.
The introduction of permanent anodes, that is anodes made of materials resistant to anodic corrosion and dissolution, represents a considerable technological improvement as these anodes offer a practically unlimited performance, or, in any case, a much longer life than the so called sacrificial anodes, which, being anodically dissolved, although offering more or less extended periods of operation, are always bound to be periodically renewed.
The new permanent anodes are usually constituted by a valve metal base, such as titanium, tantalum, niobium, hafnium, tungsten or zirconium or alloys thereof.
The anodes surface is, at least partially, coated with a layer of a material resistant to corrosion and anodically non passivatable, such as a noble metal belonging to the platinum group, such as platinum, iridium, rhodium, ruthenium, palladium, osmium or more preferably an oxide thereof, in single form or in admixture with other materials, or constituting mixed crystal with oxides of valve metals or of other metals, preferably other transition metals.
With the advent of the new permanent anodes, which afford extremely long periods of operation, it has become of paramount importance to ensure that all the parts constituting the anode structure conform to the same characteristics of reliability and durability.
In particular, the main requirement to be met is to provide a suitable electric connection to the power supply cable, long lasting and absolutely protected from contact with the medium wherein the anodic structure is operating.
Various solutions have been proposed. Among these, U.S. Pat. No. 3,134,731 illustrates a system of connection which utilizes stuffing boxes and sealing putty. U.S. Pat. No. 2,841,413 describes a connecting method utilizing a sleeve welded at one end of the anode, the conducting strands of the power supply cable being inserted into said sleeve which is then squeezed onto the strands. The electrical connection is protected by means of an impermeable adhesive tape.
However, by utilizing auxiliary sealing materials, a perfect reproducibility and reliability of the sealing is not always achieved. Moreover, the materials used to seal the connection tend to loose their properties and efficacy with time and the performance of the anodic structure often depends on the effective life of said auxiliary means.